There is often a need to determine the geographical location of a calling party. For example, when a calling party contacts an emergency response service it is desirable to ascertain the geographical location of the calling party, thereby allowing emergency services to be dispatched or otherwise provided to the calling party in a timely manner.
Within a traditional wireline telecommunications network, determining the geographic location of a particular wireline subscriber is easy, because a physical circuit connection exists between the telecommunications exchange and the subscriber's telecommunications terminal. This physical connection inherently identifies the location of the associated wireline subscriber. Thus, for example, in response to a need to locate a wireline subscriber, the serving telecommunications exchange merely has to perform a line trace along the circuit connections to determine the location of the calling party subscriber. Alternatively, the serving telecommunications exchange can determine the directory number associated with the calling party subscriber (e.g., caller ID information). The ascertained directory number is associated with a particular access line (telephone line) that can then be translated into a geographic location.
With the popularity of mobile telecommunications increasing each year, there is an increased need for efficient and accurate locating methods and arrangements, especially for calls requesting emergency services. Indeed, within the United States of America, the Federal Communications Commission (FCC) recently mandated that all mobile telecommunications service providers provide the capability to determine the geographical location of a mobile station to within an accuracy of one hundred twenty-five (125) meters when they receive an emergency call.
Locating a subscriber in a mobile telecommunications network is much more difficult because the subscriber can move about the coverage area at will. By effectuating communication through a radio link, several of the associated mobile telecommunications exchanges can service the subscriber's mobile station during a single call. For example, a mobile station is often required to actively switch between cells during a call. This requires handover operations to occur between the mobile station (MS) and the various mobile switching centers (MSC), and/or base station controller (BSC) and associated base transceiver stations (BTSs) providing services to the cells. As a result, it is no longer sufficient to merely determine the associated directory number to ascertain the current location of the mobile station. Furthermore, no wireline circuit connection is available for purposes of ascertaining location data.
A number of methods and mechanisms have been introduced to determine the geographic location of a mobile station. For example, triangulation and/or arcuation methods that measure the signal strength received from three or more neighboring cells or base transceiver stations (BTSs) can be used to determine an approximate location of the mobile station.
Further triangulation and/or arcuation methods that measure the amount of time it takes for signals to travel between three or more neighboring cells or BTSs and the mobile station have been employed to determine an approximate location of the mobile station. For example, in certain systems, the mobile station is configured to measure a unique downlink time of arrival (TOA) for downlink signals transmitted from at least three different BTSs. The differences in the measured downlink TOAs are then processed to determine an approximate location of the mobile station. Unfortunately, a typical downlink TOA method requires significant additional processing capability within the mobile station, and/or that the mobile station provide the measured downlink TOA data to another network resource for additional processing.
As an alternative, in certain systems, the mobile station is configured to transmit a particular uplink signal to three or more BTSs or other receiving nodes, for example. Each of the receiving BTSs/nodes measures a unique uplink TOA for the uplink signal. This measured uplink TOA data is then processed to determine the approximate geographical location of the mobile station.
Unlike the downlink TOA method, this type of uplink TOA method can be accomplished without significant changes to the mobile station. For example, in certain systems, the uplink TOA method is accomplished by having the mobile station attempt a typical handover procedure. This usually does not require any changes to the mobile station. Basically, in such systems, the mobile station attempts to complete a handover operation by transmitting a plurality of standard access bursts, for example, about seventy access bursts. Certain BTSs/nodes that receive the uplink signal are configured to measure an uplink TOA based on the receipt time of the access bursts. The handover operation is not, however, completed and the mobile station remains within the service of the originally servicing BTS.
Unfortunately, there are some drawbacks associated with such an uplink TOA method and system. For example, the subscriber may experience a call or speech interruption as a result of an attempted handover operation. By way of example, in certain exemplary systems, the handover operation and corresponding measurement time for uplink TOA can last for over one-third of a second. Most subscribers can notice such a speech interruption. To make matters worse, there may be a need to conduct additional attempted handover operations if the initial handover operation fails to provide the proper quality and/or quantity of uplink signal characteristic measurements. Thus, for example, there is a potential for disturbing other calls if there are too many TOA uplink positioning events occurring at about the same time, especially when the access bursts associated therewith are transmitted by the mobiles stations at about full power (as is commonly done).
There is also an inherent burden on the associated mobile telecommunications resources to schedule and subsequently intentionally ignore handover attempts by the mobile station. These problems are further exacerbated as the number of mobile stations increases and consequently the number of attempted handover operations increases.
Moreover, even the aforementioned one-third of a second uplink signal characteristic measurement time may be inadequate, under certain conditions (e.g., no frequency hopping and a slowly moving or stationary mobile station), to optimize performance of conventional TOA measurements.
Accordingly, there is a need for improved uplink signal-based location methods and arrangements that significantly reduce or otherwise minimize the amount and/or number of interruptions detectable by the mobile station subscriber, are less burdensome on the network's resources, and provide additional measurement time.